New platinum-copper catalysts cut costs, boost green technology

New platinum-copper catalysts cut costs, boost green technology

6:21 AM, 15th October 2015
New platinum-copper catalysts cut costs, boost green technology
A new generation of platinum-copper catalysts that requires very low concentrations of platinum in the form of individual atoms.

MEDFORD/SOMERVILLE, US: A new generation of platinum-copper catalysts that require very low concentrations of platinum in the form of individual atoms to cleanly and cheaply perform important chemical reactions is reported by Tufts University researchers in the journal Nature communication.

Platinum is used as a catalyst in fuel cells, in automobile converters and in the chemical industry because of its remarkable ability to facilitate a wide range of chemical reactions. However, its future potential uses are significantly limited by scarcity and cost, as well as the fact that platinum readily binds with carbon monoxide, which ‘poisons’ the desired reactions, for example in polymer electrolyte membrane (PEM) fuel cells, which  are the leading contenders for small-scale and mobile power generation not based on batteries or combustion engines. 

The Tufts researchers discovered that dispersing individual, isolated platinum atoms in much less costly copper surfaces can create a highly effective and cost-efficient catalyst for the selective hydrogenation of 1,3 butadiene, a chemical produced by steam cracking of naphtha or by catalytic cracking of gas oil.

Butadiene is an impurity in propene streams that must be removed from the stream through hydrogenation in order to facilitate downstream polymer production. The current industrial catalyst for butadiene hydrogenation uses palladium and silver.

Copper, a relatively cheap metal, is not nearly as catalytically powerful as platinum, said Charles Sykes PhD, professor of chemistry, one of the senior authors on the paper. “We wanted to find a way to improve its performance.”

The researchers first conducted surface science experiments to study precisely how platinum and copper metals mix. “We were excited to find that the platinum metal dissolved in copper, just like sugar in hot coffee, all the way down to single atoms. We call such materials single atom alloys,” said Sykes.

The Tufts chemists used a specialized low temperature scanning tunneling microscope to visualize the single platinum atoms and their interaction with hydrogen. “We found that even at temperatures as low as minus 300 degrees F these platinum atoms were capable of splitting hydrogen molecules into atoms, indicating that the platinum atoms would be very good at activating hydrogen for a chemical reaction,” Sykes said.

With that knowledge, Sykes and his fellow chemists turned to long-time Tufts collaborator Maria Flytzani-Stephanopoulos, PhD, the Robert and Marcy Haber Endowed professor, to determine which hydrogenation reaction would be most significant for industrial applications. The answer, she said, was butadiene.

The model catalyst performed effectively for that reaction in vacuum conditions in the laboratory, so Maria’s team took the study to the next level. They synthesized small quantities of realistic catalysts, such as platinum-copper single atom alloy nanoparticles supported on an alumina substrate, and then tested them under industrial pressure and temperatures.

“To our delight, these catalysts worked very well and their performance was steady for many days,” said Maria. This work with platinum is our first demonstration of operation in a flow reactor at industrially relevant conditions.

Further, they found that the reaction actually became less efficient when they used more platinum, because clusters of platinum atoms have inferior selectivity compared with individual atoms. “In this case, less is more,” said Maria, “which is a very good thing.”

Platinum is at the centre of many clean energy and green chemicals production technologies, such as fuel cells, catalytic converters, and value-added chemicals from bio-renewable feedstocks, less expensive platinum-copper catalysts could facilitate broader adoption of such environmentally friendly devices and processes, she added.

©Tufts University News

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